In my prior German patent document DE 37 27 464, I have described a process for producing fuel briquettes from a noncaking fine-grained carbon carrier and a pitch-containing binder in which a coke, especially petroleum coke in a sand-fine particle size range of 0.05 to 2 mm, is used. The sand-fine carbon carrier can also be composed of or can contain noncaking coal.
The fuel briquettes fabricated by this process must satisfy all of the physical requirements for such briquettes, i.e. must have sufficient stability and strength to withstand transport and storage and must remain intact during combustion. Further, they should neither burn too strongly nor burn only with a glow-type combustion. These characteristics of the briquette can be established by the compacting pressure during briquetting.
In the process described in DE 37 27 464, by and large the green briquettes, i.e. the preforms which are then fired to produce the final briquettes of sufficient strength, are generally free from caking coal. To the extent fine-grained caking coal is present, the quantity thereof is so small that it plays practically no role in the binder briquetting. The heat treatment is effected in a heated rotary kiln or tube furnace which is filled in its lower portion with sufficient sand-fine coke that the heat treatment is effected in a coke immersion.
This process has been found to be satisfactory. Fuel briquettes which are thus made satisfy all of the requirements for combustion. However, improvements are possible with respect to the long-term storage characteristics of the product. Since it is frequently necessary to store the briquettes for long periods before their combustion, the long-term storage characteristics are of major importance. With the prior art briquettes, it has been found that the mechanical strength diminishes with time and under certain ambient conditions. For example, it has been found that air tends to diffuse into the fuel briquettes and, especially upon storage of the briquettes in the open. Water can likewise penetrate into them reducing the binding strength of the petroleum and the coke binder matrix and thereby allowing mechanical deterioration of the briquettes.